Quenching-Induced Structural Distortion of Graphitic Carbon Nitride Nanostructures: Enhanced Photocatalytic Activity and Electrochemical Hydrogen Production

Engineered nanomaterials are emerging in the field of environmental chemistry. This study involves the analysis of the structural, electronic, crystallinity, and morphological changes in graphitic carbon nitride (g-C 3 N 4 ), an engineered nanomaterial, under rapid cooling conditions. X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Brunauer-Emmett-Teller, Fourier transform infrared, Raman, band gap, and Mott-Schottky analyses strongly proved that the liquid N 2 -quenched sample of g-C 3 N 4 has structural distortion. The photocatalytic efficiency of engineered g-C 3 N 4 nanostructures was analyzed through the degradation of reactive red 120 (RR120), methylene blue (MB), rhodamine B, and bromophenol as a representative dye. The photocatalytic dye degradation efficiency was analyzed by UV-vis spectroscopy and total organic carbon (TOC) analysis. The photocatalytic efficiency of g-C 3 N 4 under different quenching conditions included quenching at room temperature in ice and liquid N 2 . The degradation efficiencies are found to be 4.2, 14.7, and 82.33% for room-temperature, ice, and liquid N 2 conditions, respectively. The pseudo-first-order reaction rate of N 2 -quenched g-C 3 N 4 is 9 times greater than the ice-quenched g-C 3 N 4 . Further, the TOC analysis showed that 55% (MB) and 59% (RR120) of photocatalytic mineralization were achieved within a time duration of 120 min by the liquid N 2 -quenched g-C 3 N 4 nanostructure. In addition, the quenched g-C 3 N 4 electrocatalytic behavior was examined via the hydrogen (H 2 ) evolution reaction in acidic medium. The liquid N 2 -quenched g-C 3 N 4 catalyst showed a lower overpotential with high H 2 evolution when compared with the other two g-C 3 N 4 -quenched samples. The results obtained provide an insight and extend the scope for the application of engineered g-C 3 N 4 nanostructures in the degradation of organic pollutants as well as for H 2 evolution.